Abnormal migration behavior and segregation mechanism of Bi atoms undergoing liquid–solid electromigration
Abnormal migration behavior and segregation mechanism of Bi atoms undergoing liquid–solid electromigration
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DOI：
10.1007/s10853-019-03448-1
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发表时间：
2019-02
影响因子：
4.5
通讯作者：
Z. J. Zhang;M. Huang
中科院分区：
文献类型：
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作者：
Z. J. Zhang;M. Huang
使用同步辐射实时成像技术原位观察了 Cu/Sn-58Bi/Cu 焊料互连中 Bi 原子在液-固电迁移 (L-S EM) 中的迁移行为。 Bi原子倾向于从阴极向阳极迁移，导致阳极处富Bi相层在加热和冷却阶段线性生长，但在停留阶段则不然。由于 Sn-Bi 焊料在停留阶段的温度高于加热和冷却阶段的温度，因此电驱动迁移效应随着温度的升高而减弱。结果，在 140°C 的停留阶段，在焊料上观察到富 Bi、Sn-Bi 和富 Sn 相的三层平衡分布，在 170°C 的更高温度的停留阶段，观察到焊料上均匀的 Bi 分布，即 Bi 原子在如此高的温度下完全向后扩散。 Bi原子的异常迁移行为是由化学势梯度诱导通量（Jchem）和电磁诱导通量（Jem）的共同作用决定的。电磁感应通量 (Jem) 由 Bi 原子的有效电荷数 (Z*) 决定，根据富 Bi 层的生长动力学，在 140 °C 时计算为 - 3.57。此外，利用改进的液态金属Z*计算模型计算出Bi原子的Z*值为- 3.04，与实验值吻合较好。本工作为从合金中提纯难熔金属提供了参考。
The migration behavior of Bi atoms in Cu/Sn–58Bi/Cu solder interconnects undergoing liquid–solid electromigration (L–S EM) was in situ observed using synchrotron radiation real-time imaging technology. Bi atoms tend to migrate from the cathode toward the anode resulting in the linear growth of Bi-rich phase layer at the anode in both the heating and cooling stages but not in the dwelling stage. Since the temperature of Sn–Bi solder in the dwelling stage is higher than those in both the heating and cooling stages, the electrically driven migration effect diminishes with increasing temperature. As a result, a three-layer equilibrium distribution of Bi-rich, Sn–Bi and Sn-rich phases across the solder is observed in the dwelling stage of 140 °C, and a uniform Bi distribution across the solder is observed in the dwelling stage of a higher temperature of 170 °C, i.e., Bi atoms fully diffuse backward at such a high temperature. The abnormal migration behavior of Bi atoms is determined by the combined effect of chemical potential gradient-induced flux (Jchem) and EM-induced flux (Jem). The EM-induced flux (Jem) is determined by the effective charge number (Z*) of Bi atoms that is calculated as − 3.57 at 140 °C based on the growth kinetics of the Bi-rich layer. Furthermore, theZ*value of Bi atoms is calculated as − 3.04 by using a modified model for calculatingZ*of liquid metals, which agrees well with the experimental value. The present work provides a reference for purifying refractory metals from alloys.